Apparatus for quantitatively detecting foreign particles present in atmospheric air



- July 22, 1969 L. J. GOLDBERG 3,457,407 APPARATUS FOR QUANTITATIVELY DETECTING FOREIGN PARTICLES PRESENT IN ATMOSPHERIC AIR Filed July 27, 1966 ATTORNEY.

United States Patent 3,457,407 APPARATUS FOR QUANTITATIVELY DETECT- ING FOREIGN PARTICLES PRESENT IN AT- MOSPHERIC AIR Leonard J. Goldberg, Pleasant Hill, Calif., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed July 27, 1966, Ser. No. 568,361 Int. Cl. G01n 21/26; G02b 5/30 US. Cl. 25071 3 Ciairns ABSTRACT OF THE DISCLOSURE Foreign matter in the atmosphere, such as smog, can be quantitatively analyzed by causing the air to flow at a controlled rate past a particular locus of a detecting apparatus. A first elliptical mirror is used to focus light onto said locus, the light source being mounted at the first focal point of this mirror and said'locus being at its second focal point. A second elliptical mirror is disposed at right angles to the first mirror with its first focal point also at said locus. Particles in said air flow thus are illuminated and light reflected from the particles is refocussed by the second mirror. A phototube is disposed at the second focal point of the second mirror to quantitatively analyze the refocussed reflections.

The present invention relates to a particle detection apparatus and more particularly to a highly sensitive apparatus which can be used to detect fluorescent particles.

Research scientists have long desired an apparatus that would have the capability of detecting particles in a sample fluid. Some systems have been developed but have not supplied the researcher with a sufficient versatility as some circumstances dictate. Particle detection devices have considerable use in laboratory experiments in which it is desired to know the quantity of suspended particles in a known or unknown fluid. In a problem area of more pressing and practical consequences is the detection of smog emitters. In many of the large urban areas rapid industrial growth has brought about serious polution of the air. Since polution of the air is a health hazard, it is highly desirable that some form of smog control be devised. Such control would, of necessity, need to pinpoint those industries and other devices causing air pollution.

The present invention represents a great step forward in that it provides a means to determine the source of smog and other air pollution. Air pollution generally is achieved by dispensing great volumes of noxious gases and particles into the air around an urban area. The present invention may be used in combination with a seeding procedure. That is, a suspected air pollution emitter is seeded with fluorescent particles small enough so that as pollution is emitted into the air the small seeded particles will be carried along and be distributed in a fashion similar to that of the polluting gases. The present invention provides a highly sensitive detection apparatus which can be used to detect where these fluorescent particles are located. From the data obtained it may then be determined whether the suspected source is a contributor to the air pollution problem in a certain area and how great a contributor. Particle detection is achieved by illuminating a second focal point of an elliptical mirror with an illuminator located at the first focal point of the mirror. By causing an air sample to be passed through the second focal point, and by having a second elliptical mirror, which has one of its focal points coincident with the second focal point of the first elliptical mirror, illumination from a fluorescent particle will be reflected by the second elliptical mirror. A sensing "ice means located within the optical path of the second mirror can provide the necessary detection. The present invention may also be used to detect small particles which may be used by an enemy in carrying out biological warfare.

One of the objects of the present invention is to provide a highly sensitive fluorescent particle detection apparatus which is simple and very reliable.

Another object is to provide a particle detection apparatus which is capable of detecting particles as small as 0.1 in diameter.

A further object is to provide a compact detection apparatus which is easily movable so as to be able to detect the particles at various locations.

Still another object is to provide a detection apparatus which is easy to construct and economical in operation.

Yet another object is to provide a method of enabling determination of concentration of gases and/or particles from a source.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing wherein:

FIG. 1 is a side section view of a preferred embodiment of the present invention;

FIG. 2 is a front view of the embodiment.

Referring now to the drawing wherein like reference numerals designate like or corresponding parts, there is shown in FIG. 1 a highly sensitive detection apparatus 10 which may be used for detecting fluorescent particles. The detection apparatus comprises a support means 11 which may be either an enclosed structure or an open frame arrangement. A first elliptical mirror 12 connected to the support at one end thereof has a first focal point P and a second focal point F An illuminator 13 such as a watt short are mercury lamp is positioned at focal point P and connected to the support means 11 by a threaded plug 14 at the illuminators upper end and a receptacle 15 at the lower end, the receptacle being bolted to support means 11. Every elliptical mirror has the physical property of having two focal points so that light at one focal point is always focused at the second focal point, in the present invention at F FIG. 1. Bonded into counterbore 16 between F and F are filters 17 so that the light given off from illuminator 13 and reflected from the elliptical mirror 12 is concentrated at P as filtered ultraviolet light.

A second elliptical mirror 18 is supported within the apparatus so that its first focal point coincides with the second focal point of the first elliptical mirror 12. Thus F represents the second focal point of the first elliptical mirror 12 and the first focal point of the second elliptical mirror 18. Any illumination which may result at P will be reflected by the second elliptical mirror 18, to a second focal point P of the second elliptical mirror. Located at F may be a sensing means 20 which can be comprised of a photomultiplier electron tube suitably connected within aperture 21. Light directed to the sensing means 20 may be amplified and indicated on a conventional electronic instrument, not shown. Located between F and F may be filters 22 retained Within counterbore 23 which alter the quality of light before it is directed upon the sensing means 20. By placing a second elliptical mirror 18 at substantially right angles to the first elliptical mirror 12, optimum use is made of its reflecting surface so as to more efiiciently reflect light from a source at P It is to be understood that the above described focal point relationship of the mirrors 12 and 18 could be changed and the invention would still operate for its intended purposes.

Conduits 24 and 26, FIG. 2, may communicate the detection apparatus 10 with an ambient fluid so as to enable the fluid to flow past focal point F The fluid may be forced through the conduits 24 and 26 by a blower if the apparatus is stationary or the apparatus 10 may be mounted on a vehicle which in its movement will cause air to flow through conduits 24 and 26 past F Alternatively, the elements of the invention may be mounted in an open frame so that focal point P will be exposed to a circulating fluid. Optimum results are achieved if the velocity of the sampling fluid approximates a flow rate of 10 liters per minute through the apparatus 10. The detection apparatus is so compact that it can be easily 10 mounted on and carried by a vehicle such as an aircraft with conduit 24 located parallel to the direction of travel. Observation means 28 located at the end of support means 11 opposite mirror 12 provides a direct view of the detection of particles.

The use of an elliptical mirror, such as mirror 12, enables a high concentration of light from illuminator 13 to be concentrated at a relatively small area about'F Positioning two elliptical mirrors so that the second focalpoint of the first mirror coincides with a first focal point of the second mirror and illuminating the second focal point of the first mirror (which is the same as the firstfocal point of the second mirror) enables sensing of particle illumination reflected from the second mirror. The method of particle detection at a remote location from a source can be broadened to include gas detection when a seeding operation is combined with the above steps. Seeding the source of the gas with fluorescent particles, which are small enough to be transportable in the flow from the gas source, allows gas detection to be achieved. Seeding a non-fluorescent particle source with fluorescent particles may also be done to achieve particle detection.

The methods described above will not only detect particles and/or gases but will also indicate concentrations of the particles and/or gases since the quantity of fluorescent particles is also detectable with the method of the present invention.

Operation In operation the particle detection device may be mounted on a vehicle such as an aircraft and disposed so that conduit 24, FIG. 2, is facing in the direction of travel in unobstructed communication with the sampling fluid which may be atmospheric air. The sampling fluid 4,3 entering through conduit 24 will pass through an area about F FIG. 1, and then proceed out of the particle detection apparatus by way of conduit 26. Focused at F: which is the second focal point of the elliptical mirror 12 is a high concentration of filtered ultraviolet light, the source of which is illuminator 13 located at the first focal point of the elliptical mirror 12. Detection at F occurs when a fluorescent particle of a size 0.1 micron diameter or larger passes so as to cause illumination from the particle to be directed upon the second elliptical mirror 18. Since the second elliptical mirror 18 is so disposed so that its first focal point coincides with point P which is the second focal point of the first elliptical mirror 12, any illumination from a fluorescent particle at P will be incident upon elliptical mirror 18 which, in turn, concentrates the reflection at its second focal point F as indicated by the arrows. Placement of the photomultiplier electron tube sensing means 20 at P enables the detection apparatus to provide the desired information.

Obiously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim: 1. Apparatus for quantitatively detecting foreign particles present in atmospheric air comprising:

a closed support housing, a first elliptical mirror mounted in said housing, a light source mounted in the housing at a first focal point of the first mirror, a second elliptical mirror mounted in the housing at a right angle relationship with the first miror, said second mirror being so disposed that its first focal point coincides as a common point with the second focal point of the first mirror, a phototube mounted in the housing at the second focal point of said second mirror, and a pair of spaced axially-aligned open-ended conduits mounted on the housing with their aligned axis crossing said common focal point, whereby a controlled relative movement between said apparatus and atmospheric air produces an air flow in the form of a tunnel past said common focal point; light from said source then being reflected from said foreign particles in said tunnel onto said second mirror for refocussing and detection by said phototube. 2. The apparatus of claim 1 wherein said light source is an ultra-violet radiator, said apparatus further including ultra-violet filter means disposed between the first and second focal points of said first mirror for causing said common focal point to be illuminated by ultra-violet radiation. 3. A method of quantitatively analyzing foreign particles present in atmospheric air comprising,

promoting a controlled flow of air through a pair of spaced axially-aligned conduits to provide an air tunnel, focussing light onto the longitudinal axis of said tunnel and refocussing light reflected by said foreign particles in said controlled flow into a phototube.

References Cited UNITED STATES PATENTS 2,551,542 5/1951 Marsh et al. 250-71 2,932,741 2/ 1957 McKay 250-435 2,984,744- 5/ 1961 Lynch et al. 250-71 ARCHIE R. BORCHELT, Primary Examiner SAUL ELBAUM, Assistant Examiner US. Cl. X.R. 250-435, 218; 350-147; 356-103, 207 

